I bought my RO/DI unit about 3 months ago. I just got a TDS meter last week. My TDS readings out of my unit are 024ppm. Is this acceptable? At what point do you replace the cartridges? My tap water is 394 if that makes a difference.

That is high for tap ,but obviously considered safe..I think 500 is the limit for drinking/using..
We are very fortunate to only have a TDS reading of 35-40...I don't even use an RO/DI water/unit..We do have a whole house Culligan system that removes heavy metals and the chlorine.. Not TDS though
I do not have full reefs but the shrooms and rics i have do just fine,,but they'd grow in much worse conditions i'm sure

__________________
Currently rebuilding
QTing is a good thing
Grow your filtration

So a RO membrane is between 90% (100 gpd) and 99% effective for rejection rates. At 394 out of the tap, 24 ppm is ok for RO. If you also have a DI filter then the output should be 0 - 3.

My tap runs between 185 and 230 on the tds meter. I have a 150 gpd membrane rated at 99% and my RO water normally tests at 0 - 2. Anytime I see >0 after the DI I replace the DI resin.

First recheck the way you have it set up. If your unit is only 3 months old you should check with the place you bought it from.

One other thought, do you know anyone else with a RODI unit? Check your meter against their unit and their meter against your unit to make sure the meter is not the problem.
How many stages do you have, and do you have a DI filter?

I too am running a unit from pure water club. The 150gpd unit. My tap water reads 170-190 and after RO/DI my readings are 0. I have been running the unit about 4 or 5 months now. I usually make about 40gal. of RO twice a week. I use an inline tds meter and flush the system before and after every use. Seems to be working great always have a tds of 0